The present invention relates to a process for refining aluminum using segregation solidification process of molten aluminum.
Heretofore, various process have been proposed for refining metal such as aluminum using segregation solidification process of molten metal as disclosed in U.S. Pat. No. 3,671,229, for example. The process disclosed in this patent comprises the steps of penetrating a vertically movable cooling blind tube made of graphite and cooled by compressed gas circulated therein into the molten metal contained in a graphite vessel which is closed by a cover so as to maintain the atmosphere in the vessel under the condition protected by inert gas and fitted in a steel crucible heated from the outside by a heater located in a vertical kiln through a heat insulation structure so that the molten metal in the vessel is held at an appropriate temperature, thereby permitting the molten metal to be partially crystallized into the outer surface of the cooling tube under refined or purified condition to generate purified primary crystal of the metal, scraping off the thus solidified metal from the outer surface of the cooling tube by moving downwardly on annular scraping and tamping plate arranged around the cooling tube and having therein an opening of the cross-sectional configuration substantially complementary to that of the cooling tube thereby depositing the scraped metal into the bottom of the graphite vessel, then tamping or compacting the deposited metal by the scraping and tamping plate so as to press out impure liquid existing within the tamped metal upwardly above the tamped metal, while the tamped metal is partially molten so that purified crystal of the metal is rendered to grow.
In such a process, however, the cooling surface area of the cooling tube is relatively small and is gradually reduced, because the cooling tube must be raised gradually as the level of the tamped metal rises in the course of the partial crystallization, scraping and tamping operation of the metal, while the level of the molten metal in the vessel is substantially held constant thereby lowering the efficiency of refining the metal. Further, the scraping and tamping plate might move out from the lower end of the cooling tube when the scraping and tamping plate is lowered for the tamping of the deposited metal.